Sewage discharged from various drain pipes such as a residential facility, an agricultural facility, a public facility and an industrial facility is collected from a primary drain pipe to a drainage well, a sewer pipe or a sewage main pipe and a branch drain pipe and is directly discharged to a river or sea or sewage is collected in a sewage treatment facility such as a sewage end treatment plant or a sewage disposal plant and is discharged to a river or a public water surface such as sea.
A primary drain pipe or a sewage main pipe and a branch drain pipe generally installed at a sewage treatment plant as such have proper standards for the purpose of enough treating a normal amount of sewage expected in a corresponding facility or a place.
In case of a sewage discharge, a primary drain pipe or a sewage main pipe and a branch drain pipe are designed to discharge sewage in an open water passage type having a free water surface; however if influent exceeds a treatment capacity (discharging capacity) of a drain pipe per hour as heavy rain or concentrated heavy rain falls in some areas, such pipes discharge sewage in a full water state without leaving a free water surface.
So, the influent, which was not discharged through a corresponding drain pipe, overflows over a road or a ground surface, and at the same time, a discharge water pressure of a drain pipe passage rises and flows back toward a primary drain pipe where is lower than other areas, thus consequently flowing back to a drainage part and a water collection tank of a house or a public facility and an industrial facility which are sewage discharge places, thus causing a flooding damage and flooding a road or a water purification tank and other facilities.
In addition, in case that a branch drain pipe becomes a pipe water passage due to heavy fall or concentrated heavy rain in a certain area or the water level of a river sharply rises for a short time, and in case that the water level of a river rises for a long time due to seasonal rain, or in case that the water level of sea rises, the sewage and river water or sea water flow back toward the sewer pipes of a lower area or a branch drain pipe or toward an agricultural passage of a water canal, thus causing a flooding damage.
In recent years, various sewage backflow prevention apparatuses are being developed so as to preventing flooding damages due to the backflows of sewage or river water or sea water. As a sewage backflow prevention apparatus, there is ‘Apparatus for preventing reverse flow of drainage’ of the Korean patent publication number 10-2008-0078974 (hereinafter referred to the prior art).
The above mentioned prior art comprises a connection pipe connected with a drainpipe depending on the outer diameter of the drain pipe, an opening and closing part which is rotatably installed by a rotary shaft fixed at an inner side of the connection pipe and serves to open and close the pipe passage of the connection pipe, and an opening and closing part engaging shoulder which is disposed at an inner side of the connection pipe and mounts the opening and closing part which has closed the drain pipe.
The opening and closing part usually keeps closing the pipe passage of the connection pipe; however when sewage flows in from the drain pipe via the pipe passage of the connection pipe, the opening and closing part, which is installed to rotate in the direction that the sewage flows in, is open by means of the water pressure of sewage. On the contrary, when sewage flows back, the opening and closing part is closed and supported by the opening and closing part engaging shoulder, thus closing the pipe passage of the connection pipe.
Since the prior art is however characterized in that the opening and closing part is opened only by means of the water pressure of the sewage, when the amount of sewage discharged via the drain pipe is small, the opening and closing part might not be open, which leads to a problem that sewage flows back by means of the opening and closing part which was closed due to the above-mentioned problem.
As the opening and closing part interferes with the flow of sewage, a smooth discharge of sewage is hard, and since the pipe passage of the connection pipe is hard to be formed in a full open type it is almost impossible to discharge a certain object which is bulky and long.
Furthermore, when an impurity such as sand, debris, concomitant, etc. flows in via a gap between an edge portion of the opening and closing part and an inner wall of the connection pipe in a state that the opening and closing part is blocking the pipe passage, such operation might be in the middle of the operation of the opening and closing part as an interfering element, so the opening and closing part might not open.